Complex aircraft typically have one or more spoiler surfaces which are moved by a spoiler actuator. The spoilers, like any other aircraft control surface, are utilized to alter the aerodynamic configuration of the aircraft for various control purposes, usually by interfering with airflow to increase drag and/or decrease lift. As a consequence, an extended spoiler will have a marked effect on a flight characteristic of any given aircraft and will reduce the control options available to the pilot flying the aircraft.
Because of this fact, as a safety factor, in the event there is a power interruption to the actuating system for the spoiler, the spoiler must be able to be blown down by the airstream passing over it to a neutral aerodynamic position where it will not appreciably affect drag or lift and thus interfere with subsequent flight maneuvers. Thus, conventional spoiler actuation systems employ a hydraulic cylinder to extend the spoiler together with a valve which opens after a power failure to release the trapped column of hydraulic fluid that would otherwise keep the spoiler extended to allow the airstream to blow the spoiler back to an aerodynamically neutral position.
It is also highly desirable that the spoiler be held against further extension once it has been blown back to neutral aerodynamic position so that it cannot subsequently interfere with flight maneuvers by detracting from favorable flight characteristics.
State of the art design techniques for modern aircraft favor removal of hydraulic power inside the wings of an aircraft and replacing it with electromechanical actuation systems. Thus, a motor and a ball screw replace each hydraulic cylinder so that electrical energy to the motor can drive the spoilers through the ball screw. Of course, such a system still requires some sort of means to allow the spoiler to blow down to an aerodynamically neutral position and to hold it against subsequent extension.
One solution has been to use a ratchet and pawl mechanism. A solenoid holds the pawl out of engagement with the ratchet during normal operation. If a power interrupt occurs, the solenoid also loses power and releases the pawl to move into engagement with the ratchet. This technique works satisfactorily in a situation where the actuator happens to be retracting the spoiler at the time that power loss occurs. However, if the actuator is extending the spoiler, the pawl could engage the ratchet, which typically will be rotating, with a sudden and large impact load. This raises the possibility that the ratchet or the pawl could be severely damaged or even destroyed. Thus, there is a real need for a provision of a means to delay ratchet-pawl engagement in such a system until such time as the inertial impact between the two can be minimized. The present invention is directed to meeting this need.